Regular expressions are archaic-looking, extremely specific, and amazingly helpful for finding the right data, files or whatever else you need. RegEx, a free online regular expression tester, lets you hone your expression language and terms down, giving you a box to put testing text in and highlighting the words that match your query. For users of Mac OS X, Linux, or even Windows with Cygwin installed, this web-based workshop (or desktop version) is a great way to get uninhibited but real practice at file-sifting. RegEx's desktop versions require the Adobe AIR platform installed to run.